Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 EST.
1 <refentry id="func-open"> 2 <refmeta> 3 <refentrytitle>V4L2 open()</refentrytitle> 4 &manvol; 5 </refmeta> 6 7 <refnamediv> 8 <refname>v4l2-open</refname> 9 <refpurpose>Open a V4L2 device</refpurpose> 10 </refnamediv> 11 12 <refsynopsisdiv> 13 <funcsynopsis> 14 <funcsynopsisinfo>#include <fcntl.h></funcsynopsisinfo> 15 <funcprototype> 16 <funcdef>int <function>open</function></funcdef> 17 <paramdef>const char *<parameter>device_name</parameter></paramdef> 18 <paramdef>int <parameter>flags</parameter></paramdef> 19 </funcprototype> 20 </funcsynopsis> 21 </refsynopsisdiv> 22 23 <refsect1> 24 <title>Arguments</title> 25 26 <variablelist> 27 <varlistentry> 28 <term><parameter>device_name</parameter></term> 29 <listitem> 30 <para>Device to be opened.</para> 31 </listitem> 32 </varlistentry> 33 <varlistentry> 34 <term><parameter>flags</parameter></term> 35 <listitem> 36 <para>Open flags. Access mode must be 37 <constant>O_RDWR</constant>. This is just a technicality, input devices 38 still support only reading and output devices only writing.</para> 39 <para>When the <constant>O_NONBLOCK</constant> flag is 40 given, the read() function and the &VIDIOC-DQBUF; ioctl will return 41 the &EAGAIN; when no data is available or no buffer is in the driver 42 outgoing queue, otherwise these functions block until data becomes 43 available. All V4L2 drivers exchanging data with applications must 44 support the <constant>O_NONBLOCK</constant> flag.</para> 45 <para>Other flags have no effect.</para> 46 </listitem> 47 </varlistentry> 48 </variablelist> 49 </refsect1> 50 <refsect1> 51 <title>Description</title> 52 53 <para>To open a V4L2 device applications call 54 <function>open()</function> with the desired device name. This 55 function has no side effects; all data format parameters, current 56 input or output, control values or other properties remain unchanged. 57 At the first <function>open()</function> call after loading the driver 58 they will be reset to default values, drivers are never in an 59 undefined state.</para> 60 </refsect1> 61 <refsect1> 62 <title>Return Value</title> 63 64 <para>On success <function>open</function> returns the new file 65 descriptor. On error -1 is returned, and the <varname>errno</varname> 66 variable is set appropriately. Possible error codes are:</para> 67 68 <variablelist> 69 <varlistentry> 70 <term><errorcode>EACCES</errorcode></term> 71 <listitem> 72 <para>The caller has no permission to access the 73 device.</para> 74 </listitem> 75 </varlistentry> 76 <varlistentry> 77 <term><errorcode>EBUSY</errorcode></term> 78 <listitem> 79 <para>The driver does not support multiple opens and the 80 device is already in use.</para> 81 </listitem> 82 </varlistentry> 83 <varlistentry> 84 <term><errorcode>ENXIO</errorcode></term> 85 <listitem> 86 <para>No device corresponding to this device special file 87 exists.</para> 88 </listitem> 89 </varlistentry> 90 <varlistentry> 91 <term><errorcode>ENOMEM</errorcode></term> 92 <listitem> 93 <para>Not enough kernel memory was available to complete the 94 request.</para> 95 </listitem> 96 </varlistentry> 97 <varlistentry> 98 <term><errorcode>EMFILE</errorcode></term> 99 <listitem> 100 <para>The process already has the maximum number of 101 files open.</para> 102 </listitem> 103 </varlistentry> 104 <varlistentry> 105 <term><errorcode>ENFILE</errorcode></term> 106 <listitem> 107 <para>The limit on the total number of files open on the 108 system has been reached.</para> 109 </listitem> 110 </varlistentry> 111 </variablelist> 112 </refsect1> 113 </refentry>
